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Abstract:

An image forming apparatus includes an ink jet head, having a pressure
chamber, a flow path and a nozzle, which ejects ink in the pressure
chamber through the nozzle, a first tank connected to the flow path, a
supply unit which supplies ink in the first tank to the pressure chamber
through the flow path, a second tank connected to the flow path, a
discharge unit which moves ink in the pressure chamber to the second tank
through the flow path, and a control section which activates the supply
unit and the discharge unit so that ink in the pressure chamber is
discharged to the second tank by the discharge unit, ink in the first
tank is charged to the pressure chamber by the supply unit and the liquid
surface of ink supplied to the pressure chamber is projected from the
nozzle.

Claims:

1. An image forming apparatus comprising: an ink jet head, including a
pressure chamber to which ink is charged, a flow path fluidly
communicating with the pressure chamber and a nozzle open to the pressure
chamber, which is configured to eject ink in the pressure chamber from
the nozzle; a first tank, connected to the flow path of the head, which
is configured to store ink; a supply unit configured to supply the ink in
the first tank to the pressure chamber of the head through the flow path
of the head; a second tank, connected to the flow path of the head, which
is configured to store ink; a discharge unit configured to move the ink
in the pressure chamber of the head to the second tank through the flow
path of the head; and a control section configured to activate the supply
unit and the discharge unit so that the ink in the pressure chamber is
discharged to the second tank by the discharge unit, the ink in the first
tank is charged to the pressure chamber by the supply unit and the liquid
surface of the ink supplied to the pressure chamber is projected from the
nozzle of the head.

2. The apparatus according to claim 1, wherein the discharge unit moves
the ink in the pressure chamber of the head to the second tank by
decreasing the pressure in the nozzle of the head.

3. The apparatus according to claim 2, wherein the discharge unit
decreases the pressure in the nozzle by increasing the height difference
in the liquid surface between the ink in the nozzle of the head and the
ink in the second tank.

4. The apparatus according to claim 3, wherein the discharge unit
increases the height difference in the liquid surface between the ink in
the nozzle of the head and the ink in the second tank by moving the
second tank to a position lower than that of the head.

5. The apparatus according to claim 3, wherein the discharge unit
includes a pump which discharges the ink in the second tank to decrease
the liquid surface of the ink stored in the second tank, and increases
the height difference in the liquid surface between the ink in the nozzle
of the head and the ink stored in the second tank.

6. The apparatus according to claim 4, wherein the head includes a drive
element which pressurizes the ink supplied to the pressure chamber to
project the liquid surface of the ink in the pressure chamber to the
outside of the head by pressurizing the ink supplied to the pressure
chamber by the drive element.

7. The apparatus according to claim 6 further comprising a circulation
path connected between the first tank and the second tank, and a
circulation pump configured to convey the ink stored in the second tank
arranged at the circulation path.

8. The apparatus according to claim 5, wherein the head includes a drive
element which pressurizes the ink supplied to the pressure chamber to
project the liquid surface of the ink in the pressure chamber to the
outside of the head by pressurizing the ink supplied to the pressure
chamber by the drive element.

9. The apparatus according to claim 6 further comprising a circulation
path connected between the first tank and the second tank, and a
circulation pump configured to convey the ink stored in the second tank
arranged at the circulation path.

10. An image forming apparatus comprising: an ink jet head, having a
pressure chamber to which ink is charged and a nozzle open to the
pressure chamber, which is configured to eject ink in the pressure
chamber from the nozzle; a first unit configured to supply ink to the
pressure chamber of the head; a second unit configured to suck the ink
charged to the pressure chamber so as to move the liquid surface of the
ink formed in the nozzle of the head to the inside of the pressure
chamber; and a control section configured to activate the first unit and
the second unit so that the ink in the pressure chamber is discharged by
the second unit, and a flesh ink is charged to the pressure chamber by
the first unit to project the liquid surface of the flesh ink from the
nozzle of the head.

11. A method for performing maintenance of an image forming apparatus,
comprising an ink jet head, having a pressure chamber to which ink is
charged, a flow path fluidly communicating with the pressure chamber and
a nozzle open to the pressure chamber, which is configured to eject ink
in the pressure chamber from the nozzle, a first tank, connected to the
flow path of the head, which is configured to store ink, a supply unit
configured to supply the ink in the first tank to the pressure chamber of
the head through the flow path of the head, a second tank, connected to
the flow path of the head, which is configured to store ink, a discharge
unit configured to move the ink in the pressure chamber of the head to
the second tank through the flow path of the head, and a control section
configured to activate the supply unit and the discharge unit, which
includes: discharging the ink in the pressure chamber to the second tank
by the discharge unit; charging the ink in the first tank to the pressure
chamber by the first unit; and projecting the liquid surface of the ink
supplied to the pressure chamber from the nozzle of the head.

12. The method according to claim 11, wherein the discharge unit moves
the ink in the pressure chamber to the second tank by decreasing the
pressure in the nozzle of the head.

13. The method according to claim 12, wherein the discharge unit
decreases the pressure in the nozzle by increasing the height difference
in the liquid surface between the ink in the nozzle of the head and the
ink in the second tank.

14. The method according to claim 13, wherein the discharge unit
increases the height difference in the liquid surface between the ink in
the nozzle of the head and the ink in the second tank by moving the
second tank to a position lower than that of the head.

15. The method according to claim 13, wherein the discharge unit includes
a pump which discharges ink in the second tank to decrease the liquid
surface of the ink stored in the second tank, and increases the height
difference in the liquid surface between the ink in the nozzle of the
head and the ink stored in the second tank.

16. The method according to claim 15, wherein the head includes a drive
element which pressurizes the ink supplied to the pressure chamber and
the drive element projects the liquid surface of the ink in the pressure
chamber to the outside of the head by pressurizing the ink supplied to
the pressure chamber.

17. The method according to claim 16, wherein the image forming apparatus
comprises a circulation path connected between the first tank and the
second tank, a circulation pump, arranged at the circulation path, which
conveys the ink stored in the second tank to the first tank, including:
Conveying the ink discharged to the second tank by the discharging unit
is conveyed to the first tank by the circulation pump through the
circulation path.

18. The method according to claim 15, wherein the head includes a drive
element which pressurizes the ink supplied to the pressure chamber and
the drive element projects the liquid surface of the ink in the pressure
chamber to the outside of the head by pressurizing the ink supplied to
the pressure chamber.

19. The method according to claim 18, wherein the image forming apparatus
comprises a circulation path connected between the first tank and the
second tank, a circulation pump, arranged at the circulation path, which
conveys the ink stored in the second tank to the first tank, including:
Conveying the ink, that is discharged to the second tank by the
discharging unit, to the first tank by the circulation pump through the
circulation path.

Description:

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is based upon and claims the benefit of priority
from the prior Japanese Patent Application No. 2012-060923, filed on Mar.
16, 2012, the entire contents of all of which are incorporated herein by
reference.

FIELD

[0002] The present embodiments relate an image forming apparatus and a
method for performing maintenance of the ink jet head of the image
forming apparatus.

BACKGROUND

[0003] An image forming apparatus such as an ink jet printer ejects ink
from the nozzle provided on the ink jet head to form an image. The ink
may be coagulated or caked when viscosity thereof is increased because of
evaporation of the liquid component and the volatile component of the
ink. If ink is caked within the nozzle, it may course failure of
printing.

[0004] To restrain the failure of printing with the caked ink, it is well
known, for example, that pressure applied to the ink in the ink jet head
is varied to flow ink nearby the nozzle. The ink is stirred with the flow
of ink and thus the coagulation of the ink is restrained.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Aspects of this disclosure will become apparent upon reading the
following detailed description and upon reference to the accompanying
drawings. The description and the associated drawings are only provided
to illustrate embodiments of the invention and not limited to the scope
of the invention, wherein:

[0006]FIG. 1 is a block diagram roughly illustrating construction of a
printing apparatus according to a first embodiment;

[0007]FIG. 2 is an exploded perspective view illustrating an ink jet head
according to the first embodiment;

[0008]FIG. 3 is a sectional view illustrating the ink jet head, taken
along the lines F3-F3 of FIG. 2;

[0009]FIG. 4 is a flow chart showing one example of a method for
performing maintenance of the printing apparatus shown in FIG. 1;

[0010]FIG. 5 is a block diagram roughly showing the printing apparatus at
a state that a meniscus is pulled back;

[0011]FIG. 6 is a sectional view illustrating the pressure chamber and
the nozzle of the ink jet head;

[0012]FIG. 7 is a sectional view illustrating a state in which the
meniscus is withdrawn from the nozzle in the ink jet head;

[0013]FIG. 8 is a sectional view illustrating a state in which the
meniscus is further withdrawn from the state shown in FIG. 7 in the ink
jet head;

[0014]FIG. 9 is a sectional view illustrating a state in which the
meniscus is sill further withdrawn from the state shown in FIG. 8 in the
ink jet head;

[0015]FIG. 10 is a sectional view illustrating a state in which the
meniscus is further withdrawn from the state shown in FIG. 9 in the ink
jet head;

[0016]FIG. 11 is a sectional view illustrating the empty pressure chamber
and nozzle of the ink jet head;

[0017]FIG. 12 is a sectional view illustrating a state in which ink is
supplied to the pressure chamber in the ink jet head;

[0018]FIG. 13 is a sectional view illustrating a state in which ink is
further supplied to the pressure chamber from the state shown in FIG. 12
in the ink jet head;

[0019]FIG. 14 is a sectional view illustrating a state in which ink is
charged in the pressure chamber in the ink jet head;

[0020]FIG. 15 is a sectional view illustrating the ink jet head in which
a purge operation is performed;

[0021]FIG. 16 is a flow chart illustrating another example of the
maintenance method in the printing apparatus; and

[0022]FIG. 17 is a block diagram roughly illustrating construction of a
printing apparatus according to a second embodiment.

DETAILED DESCRIPTION

[0023] In general, according to one embodiment, it is to provide an image
forming apparatus including an ink jet head, having a pressure chamber in
which ink is filled, a flow path fluidly communicating with the pressure
chamber and a nozzle open to the pressure chamber, which is configured to
eject the ink in the pressure chamber through the nozzle, a first tank
connected to the flow path of the head to store ink, a supply unit
configured to supply the ink in the first tank to the pressure chamber of
the head through the flow path of the head, a second tank connected to
the flow path of the head to store ink, a discharge unit configured to
move the ink in the pressure chamber of the head to the second tank
through the flow path of the head, and a control section configured to
activate the supply unit and the discharge unit so that the ink in the
pressure chamber is discharged to the second tank by the discharge unit,
the ink in the first tank is charged to the pressure chamber by the
supply unit and the liquid surface of the ink supplied to the pressure
chamber is projected from the nozzle of the head,

[0024] Embodiments will now be described in more detail with reference to
the accompanying drawings. However, the same numerals are applied to the
similar elements in the drawings, and therefore, the detailed
descriptions thereof are not repeated.

First Embodiment

[0025] A first embodiment will be described with reference to the FIG. 1
to the FIG. 16. FIG. 1 is a diagram roughly illustrating construction of
an ink jet printing apparatus (hereinafter referred to as a printing
apparatus) 10. The printing apparatus 10 is an example of an image
forming apparatus.

[0026] The printing apparatus 10 includes an ink jet head 11, a T-shaped
junction 13, an upper-stream side open/close valve 15, a pressure
regulation tank 17, a first filter 19, a first disposable filter 21, an
upper-stream side ink tank 23, an upper-stream side air pump 25 and a
second disposable filter 27. The printing apparatus 10 further includes a
lower-stream side open/close valve 29, a lower-stream side ink tank 31, a
third disposable filter 33, a lower-stream side suction pump 35, an
upper-stream side open/close valve 37, a lower-stream side open/close
valve 39, a tank moving mechanism 41 and a control section 43.

[0027] The ink jet head 11 is an example of a head. The pressure
regulation tank 17 is an example of a first tank. The upper-stream side
air pump 25 is an example of a supply unit. The lower-stream side ink
tank 31 is an example of a second tank. The lower-stream side suction
pump 35 is an example of a pump. The tank moving mechanism 41 is an
example of a discharge unit.

[0028]FIG. 2 is an exploded perspective view illustrating an ink jet head
11. FIG. 3 is a sectional view illustrating the ink jet head, taken along
the lines F3-F3 of the FIG. 2.

[0029] As shown in the FIG. 2, the ink jet head 11 is a so-called
shear-mode type ink jet head. The ink jet head 11 includes a head body
50, a frame member 51, a cover member 52, a nozzle plate 53 and a circuit
base plate 54.

[0030] The head body 50 includes a base member 61 and a piezoelectric
member 62. The base member 61 is formed in a rectangular plate shape and
is provided with a cut portion 64 and a plurality of grooves 65. The
plurality of grooves 65 are formed in parallel with one another. The
plurality of grooves 65 open at the upper surface 61a of the base member
61 and the cut portion 64, respectively.

[0031] The piezoelectric member 62 is formed such that two piezoelectric
plates made of lead zinconate titanate are stuck with one another. The
two piezoelectric plates are polarized in an opposite direction. The
piezoelectric member 62 is deformed by a voltage applied. The
piezoelectric member 62 is mounted on the cut portion 64 of the base
plate 61.

[0032] A plurality of pressure chambers 67 are formed on the piezoelectric
member 62. The plurality of pressure chambers 67 are respectively formed
in a groove shape and provided in parallel with one another. The
plurality of pressure chambers 67 fluidly communicate with the plurality
of grooves 65 of the base member 61 one to one manner. Each pressure
chamber 67 opens at the upper surface 62a and the front surface 62b of
the piezoelectric member 62.

[0033] A pole portion 68 is formed between pressure chambers 67, A
plurality of pole portions 68 respectively partition the plurality of
pressure chambers 67 and form the side surface of each pressure chamber
67.

[0034] As shown in the FIG. 3, a plurality of electrodes 71 are
respectively provided on the piezoelectric member 62 and the base member
61. The plurality of electrodes 71 respectively cover the side surface
and the bottom surface of the plurality of pressure chambers 67. The
plurality of electrodes 71 are continuously extended from the pressure
chamber 67 to the groove 65. The electrode 71 is formed with a thin film
of nickel, for example. However, it is not limited to this and the
electrode 71 may be made of gold or cupper. Pole portions 68 on which the
electrode 71 is formed on the both sides thereof act as an actuator.

[0035] On the other hand, as shown in the FIG. 2, a plurality of wiring
patterns 73 are formed on the upper surface 61a of the base member 61.
The plurality of wiring patterns 73 are formed, for example, such that a
thin film of nickel on the upper surface 61a of the base member 61 is
processed with patterning by a laser. The plurality of wiring patters 73
respectively extend from the rear end of the upper surface 61a of the
base member 61. Each one of the end portions of the wiring pattern 73 is
connected to the electrode 71.

[0036] The circuit base plate 54 is arranged at the other end portion of
the wiring pattern 73. The circuit base plate 54 is, for example, a film
carrier package including a plastic film on which a plurality of
conductor patterns are formed, and an IC (Integrated Circuit) Device
connected to the plurality of conductor patterns. The plurality of
conductor patterns are electrically connected to the other ends of the
plurality of wiring patterns, respectively.

[0037] The frame member 51 is mounted on the head body 50 with glue. The
cover member 52 is mounted on the frame member 51. An ink supply opening
81 is provided on the cover member 52. Such combined frame member 51 and
cover member 52 cover the plurality of pressure chambers 67 from the
upper surface 61a of the base member 61.

[0038] As shown in the FIG. 3, an ink chamber 82 to which ink is supplied
is formed in the inside of the combined frame member 51 and cover member
52. The ink chamber 82 is an example of the flow path. The cover member
52 covers the ink chamber 82 by attaching on the frame member 51. The ink
supply opening 81 is formed on the cover member 52 and is fluidly
communicated with the ink chamber 82. The ink chamber 82 is fluidly
communicated with the plurality of pressure chambers 67. Ink supplied to
the ink chamber 82 through the ink supply opening 81 is further supplied
to each pressure chamber 67.

[0039] The nozzle plate 53 is a rectangular shaped film made of polyimide
plastic. However, the nozzle plate 53 is not limited to be made of
polyimide but may be made of steel such as a stainless steel or other
material which is able to be fine-processed by a laser. The nozzle plate
53 is attached on the head body 50 and frame member 51. The nozzle plate
53 covers the plurality of pressure chambers 67 at the side of the front
surface 62b of the piezoelectric member 62.

[0040] A plurality of nozzles 85 are provided on the nozzle plate 53. The
nozzles 85 are formed by a laser processing, respectively. As shown in
the FIG. 3, the plurality of nozzles 85 open to the plurality of pressure
chambers 67, respectively.

[0041] In such an ink jet head as described above, the circuit base plate
54 applies a voltage to the electrode 71 through the wiring pattern 73
based on a print signal input from the control section 43. The pole
portion 68 to which the voltage is applied performs a shear-mode
deformation in response to the print signal. Ink to which pressure is
increased is ejected from the corresponding nozzle 85.

[0042] The ink jet head 11 is loaded in the printing apparatus 10 such
that it is supported by a head support mechanism. As shown in the FIG. 1,
one of the ends of a pipe member 101 is connected to the ink supply
opening 81 of the ink jet head 11 and the other end thereof is connected
to the T-shaped junction 13.

[0043] The pressure regulation tank 17 is connected to the upper-stream
side of the ink jet head 11 through the T-shaped junction 13 and a pipe
member 102. In other words, the pressure regulation tank 17 is connected
to the ink chamber 82 of the ink jet head 11.

[0044] The upper-stream side open/close valve 15 is arranged at the pipe
member 102 between the T-shaped junction 13 and the pressure regulation
tank 17. The upper-stream side open/close valve 15 is selectively
switched between an open position at which flow of ink from the pressure
regulation tank 17 to the ink jet head 11 is allowed and a closed
position at which flow of ink between the pressure regulation tank 17 and
the ink jet head is shut.

[0045] Ink supplied from the upper-stream side ink tank 23 is stored in
the pressure regulation tank 17, temporarily. One of the ends of the pipe
member 102 is positioned within the ink stored in the pressure regulation
tank 17 such that it is slightly apart from the bottom surface of the
pressure regulation tank 17. A first hydraulic head sensor 104 is
arranged in the pressure regulation tank 17. The first hydraulic head
sensor 104 varies its output in response to the position of the
gas-liquid boundary surface of ink and air, i.e., surface of ink, stored
in the pressure regulation tank 17. The first hydraulic head sensor 104
is a float type level sensor, for example, However, the first hydraulic
head sensor 104 may be other sensor such as a photo-sensor.

[0046] A pipe member 106 is connected to the pressure regulating tank 17.
One of the ends of the pipe member 106 is positioned within the ink
stored in the pressure regulation tank 17 such that it is slightly apart
from the bottom surface of the pressure regulation tank 17, and the other
end thereof is connected to the first filter 19.

[0047] A pipe member 107 is connected to the first filter 19. The first
filter 19 removes a foreign substance contained in the ink flowing from
the pipe member 107 located at the upper-stream side of the first filter
19 to the pipe member 106 located at the lower-stream side of the first
filter 19 thereby providing ink from which a foreign substance is removed
to the pressure regulation tank 17.

[0048] The first filter 19 is connected to the upper-stream side ink tank
23 through the pipe member 107. One end of the pipe member 107 is
positioned within the ink stored in the upper-stream side ink tank 23
such that it is slightly apart from the bottom surface of the
upper-stream side ink tank 23.

[0049] A pipe member 109 is connected to the pressure regulation tank 17.
One of the ends of the pipe member 109 is positioned within the air in
the pressure regulation tank 17 such that it is slightly apart from the
gas-liquid boundary surface (ink surface) between the ink and the air in
the pressure regulation tank 17. The other end of the pipe member 109 is
connected to the first disposable filter 21. The first disposable filter
21 removes a foreign substance contained in the air flowing into the
pressure regulation tank 17 through the pipe member 109. The upper-stream
side open/close valve 37 is provided at the pipe member 109.

[0050] The upper-stream side ink tank 23 is connected to the upper-stream
side air pump 25 through a pipe member 111. The upper-stream side ink
tank 23 stores ink supplied to the ink jet head 11. The upper-stream side
ink tank 23 is able to be supplemented with ink.

[0051] One of the ends of the pipe member 111 is positioned within the air
in the upper-stream side ink tank 23 such that it is slightly apart from
the gas-liquid boundary surface between the air and the ink. The other
end of the pipe member 111 is connected to the second disposable filter
27. The second disposable filter 27 removes a foreign substance contained
in the air flowing into the upper-stream side ink tank 23 through the
pipe member 111 thereby providing air from which a foreign substance is
removed to the upper-stream side ink tank 23.

[0052] At the lower-stream side of the ink jet head 11, the lower-stream
side ink tank 31 in which ink is stored is connected through the T-shaped
junction 13 and a pipe member 113. In more detail, the lower-stream side
ink tank 31 is connected to the ink chamber 82 of the ink jet head 11.
One end of the pipe member 113 is positioned within the ink in the
lower-stream side ink tank 31 such that it is slightly apart from the
bottom surface of the lower-stream side ink tank 31.

[0053] The lower-stream side open/close valve 29 is provided at the pipe
member 113, as shown in the FIG. 1. The lower-stream side open/close
valve 29 is selectively switched between an open position at which the
ink flow from the ink jet head 11 to the lower-stream side ink tank 31 is
allowed and a shut down position at which the ink flow between the ink
jet head and the lower-stream side ink tank 31 is inhibited.

[0054] A pipe member 115 is connected to the lower-stream side ink tank
31. One of the ends of the pipe member 115 is positioned within the air
in the lower-stream side ink tank 31 such that it is slightly apart from
the gas-liquid boundary surface, i.e., ink surface, between the air and
the ink in the lower-stream side ink tank 31. The other end of the pipe
member 115 is connected to the third disposable filter 33. The third
disposable filter 33 removes a foreign substance contained in the air
flowing into the lower-stream side ink tank 31 through the pipe member
115. The pipe member 115 is provided with the lower-stream side ink tank
39.

[0055] The lower-stream side ink tank 31 is provided with a second
hydraulic head sensor 119. The second hydraulic head sensor 119 varies
its output in response to the position of the gas-liquid boundary surface
of the ink and the air, i.e., surface of ink, stored in the lower-stream
side ink tank 31. The second hydraulic head sensor 119 is a float type
level sensor, for example, however, the second hydraulic head sensor 119
may be other sensor such as a photo-sensor.

[0056] The tank moving mechanism 41 moves the lower-stream side ink tank
31 in a vertical direction, for example. The tank moving mechanism 41
comprises a gear, a piston and other mechanism to move the lower-stream
side ink tank 31.

[0057] The control section 43 functions as hardware elements such as an
IC, a memory, a circuit board and others to control various hardware
components of the printing apparatus 10. For example, control section 43
issues a print command to the ink jet head 11 responding to the operation
by a user. The control section 43 makes the upper-stream side open/close
valve 15, the lower-stream side open/close valve 29, the upper-stream
side open/close valve 37 and the lower-stream side open/close valve 39
open or close. The control section 43 also makes the upper-stream side
air pump 25 and the lower-stream side suction pump 35 start or stop. The
control section 43 moves the lower-stream side ink tank 31 through the
ink moving mechanism 41.

[0058] In the following, a method for filling or charging ink in the ink
jet head 11 will be described with reference to the FIG. 1.

[0059] Firstly, the upper-stream side open/close valve 37 is set to the
shut down position and the upper-stream side open/close valve 15 and the
lower-stream side open/close valve 29 are set to the open position
respectively. Then, the upper-stream side air pump 25 is activated to
feed air into the upper-stream side ink tank 23. The internal pressure of
the upper-stream side ink tank 23 is increased with the air fed to the
ink tank 23. When the internal pressure of the upper-stream side ink tank
23 is increased to a given value, the ink stored in the upper-stream side
ink tank 23 is pushed out to the pipe member 107, as shown by an arrow in
the FIG. 1, with the increased internal pressure of the upper-stream side
ink tank 23.

[0060] The ink pushed out of the upper-stream side ink tank 23 is conveyed
to the first filter 19 through the pipe member 107. In the ink conveyed
to the first filter 19, a foreign substance contained in the ink is
removed while the ink passes through the first filter 19 and then the ink
is further conveyed to the pressure regulation tank 17.

[0061] When ink is filled in the pressure regulation tank 17 by a given
amount, the air in the pressure regulation tank 17 is compressed. When
the pressure in the pressure regulation tank 17 reaches at a prescribed
level, the ink in the pressure regulation tank 17 is pushed out to the
pipe member 102 with the increased internal pressure in the pressure
regulation tank 17, as shown by the arrow in the FIG. 1.

[0062] The ink pushed out of the pressure regulation tank 17 is fed to the
ink supply opening 81 of the ink jet head 11 through the pipe member 102
and the T-shaped junction 13. Then, as shown in the FIG. 3, the ink from
the ink supply opening 81 is charged to the plurality of pressure chamber
67 through the ink chamber 82, respectively. The ink charged to the
pressure chamber 67 finally reaches at the nozzle 85.

[0063] In explaining the above description with other expression, the
upper-stream side air pump 25 supplies ink in the pressure regulation
tank 17 to the pressure chamber 67 through the ink chamber 82 shown in
the FIG. 3. Furthermore, in other words, the pressure regulation tank 17,
the upper-stream side ink tank 23 and the upper-stream side air pump 25
supply ink to the pressure chamber 67. The upper-stream side ink tank 23
and the upper-stream side air pump 25 are an example of element which
functions as a supply device (first device).

[0064] When ink is filled in the pressure chamber 67, the ink pushed out
of the pressure regulation tank 17 is supplied to the lower-stream side
ink tank 31 through the pipe member 113 and the lower-stream side
open/close valve 29.

[0065] In a state that the ink jet head 11 does not eject ink, a proper
pressure (Pn) in the nozzle 85 is set to be -1 (kPa), for example, with
the hydraulic head. That is, the height difference (h1) between the
nozzle 85 of the ink jet head 11 and the gas-liquid boundary surface of
the ink in the pressure regulation tank 17 is set to be a prescribed
amount so that a formula (h1=-1(kPa)/ρg) is satisfied, wherein, ρ
is the density of ink and g is the acceleration of gravity. Besides, the
height difference (h1) is detected by the first hydraulic head sensor 104
arranged in the pressure regulation tank 17.

[0066] A height difference (h2) between the nozzle 85 of the ink jet head
11 and the gas-liquid boundary surface of the ink in the lower-stream
side ink tank 31 is set to be equal to the height difference (h1).
However, the height difference (h2) may be set to be greater than the
height difference (h1). In other words, the lower-stream side ink tank 13
is arranged at a height the same as that of the pressure regulation tank
17 or lower than that of the pressure regulation tank 17.

[0067] Next, an example of the maintenance method of the printing
apparatus 10 including the above-described construction will be described
with reference to the FIGS. 4 and 5. For example, the control section 43
executes the maintenance of the printing apparatus 10 in case that the
printing apparatus 10 is not used for a long time or the print-standby
state thereof is continued for a relatively long time.

[0068]FIG. 4 is a flow chart illustrating an example of the maintenance
method of the printing apparatus 10. FIG. 5 is a block diagram roughly
illustrating the printing apparatus 10 when the meniscus is pulled back.

[0069] As shown in the FIG. 4, in case in which the printing apparatus 10
is not used for a long time or the print-standby state thereof is
continued for a relatively long time (Act. S1), the proper pressure (Pn)
of the nozzle 85 is controlled by a well known negative pressure
generation means. A meniscus of the ink formed in the nozzle 85 is pulled
back by setting the pressure of the nozzle 85 at a negative pressure
value greater than the normal negative pressure value (-1(kPa)).

[0070] In more detail, firstly, the upper-stream side open/close valve 15
positioned between the pressure regulation tank 17 and the ink jet head
11 is set to the shut down position at which the flow of ink is prevented
(ACT S2).

[0071] Next, the lower-stream side ink tank 31 is moved downward by the
tank moving mechanism 41 (ACT S3). As shown in the FIG. 5, the height
difference (h2) between the nozzle 85 of the ink jet head 11 and the
gas-liquid boundary surface of the ink in the lower-stream side ink tank
31 is increased when the lower-stream side ink tank 31 is moved downward.

[0072] The height difference (h2) reaches, for example, at four times the
height difference (h1) between the nozzle 85 and the gas-liquid boundary
surface of the ink in the pressure regulation tank 17 (YES in ACT S4),
the tank moving mechanism 41 is stopped (ACT S5). When the height
difference (h2) reaches at four times the height difference (h1), the
proper pressure (Pn) of the nozzle 85 is to be -4(kPa). That is, when the
lower-stream side ink tank 31 is moved, the negative pressure in the
nozzle 85 is increased from the proper pressure (Pn: -1(kPa)) therein at
the standby state. The height difference (h2) is detected by the second
hydraulic head sensor 119.

[0073] By increasing the negative pressure, the ink in the ink jet head 11
flows toward the lower-stream side ink tank 31 through the pipe member
101, the T-shaped junction 13 and the pipe member 113, as shown by the
arrow in the FIG. 5. In other words, ink charged in the pressure chamber
67 of the ink jet head 11 is sucked into the lower-stream side ink tank
31.

[0074] As described above, the tank moving mechanism 41 increases the
height difference (h2) between the nozzle 85 and the ink surface in the
lower-stream side ink tank 31 by moving the lower-stream side ink tank
31. When the height difference (h2) is increased, the pressure in the
nozzle 85 is decreased and thus the ink in the pressure chamber 67 of the
ink jet head 11 moves to the lower-stream side ink tank 31 through the
ink chamber 82. In other words, the lower-stream side ink tank 31 and the
tank moving mechanism 41 suck ink charged in the pressure chamber 67. The
lower-stream side ink tank 31 and the tank moving mechanism 41 are one
example of the element which functions as a second unit.

[0075] It should be noted that the height difference (h2) at a position
that the tank moving mechanism 41 stops is not limited to the above (h2
is four times h1). The height difference (h2) may be a given degree that
the ink in the ink jet head 11 is smoothly sucked into the lower-stream
side ink tank 31.

[0076]FIG. 6 is a sectional view illustrating the pressure chamber 67 and
the nozzle 85 of the ink jet head 11. FIG. 7 is a sectional view
illustrating a state in which the meniscus M is pulled back from the
nozzle 85 of the ink jet head 11. FIG. 8 is a sectional view illustrating
a state in which the meniscus M is further pulled back from the state
shown in the FIG. 7. FIG. 9 is a sectional view illustrating a state in
which the meniscus M is still further pulled back from the state shown in
the FIG. 8. FIG. 10 is a sectional view illustrating a state in which the
meniscus M is pulled back from the state shown in the FIG. 9.

[0077] As shown in the FIG. 6, the bubble B and the caked ink SL are
contained in the ink charged in the pressure chamber 67. If the bubble B
and the caked ink SL are present in the nozzle 85, it may cause failure
of ink ejection by the ink jet head 11.

[0078] As shown in the FIGS. 6 to 10, when the ink charged in the pressure
chamber 67 is sucked, the meniscus M (liquid surface) charged in the
pressure chamber 67 is moved to the inside of the pressure chamber 67
from the nozzle 85. The bubble B and the caked ink SL presented in the
nozzle 85 are flown together with the ink because of moving the meniscus
M. The bubble B and the caked ink SL are conveyed with the flow of the
ink from the nozzle 85 to the lower-stream side ink tank 31.

[0079] With the elapse of the time, the ink charged in the pressure
chamber 67 is discharged to the lower-stream side ink tank 31 and thus
the pressure chamber 67 becomes empty. In other words, ink is discharged
from the pressure chamber 67 by the lower-stream side ink tank 31 and the
tank moving mechanism 41. Note that a certain amount of ink may be left
in the pressure chamber 31.

[0080] As shown in the FIG. 4, the control section 43 determines whether
or not the gas-liquid boundary surface of the ink, i.e., ink surface, in
the lower-stream side ink tank 31 raises by a predetermined height (ACT
S7) after a prescribed time elapses from the moving of the lower-stream
side ink tank 31. (YES in ACT S6). The predetermined time is a time
required to discharge all of the ink charged in the plurality of pressure
chambers 67 to the lower-stream side ink tank 31, for example. The
predetermined height is a height to which the ink surface raises when all
of the ink charged in the plurality of pressure chambers 67 is conveyed
to the lower-stream side ink tank 31, for example. In other words, the
control section 43 judges whether or not the pressure chamber 67 is
empty. The increasing amount of the gas-liquid boundary surface of the
ink in the lower-stream side ink tank 31 is detected by the second
hydraulic head sensor 119.

[0081] The control section 43 further moves downward the lower-stream side
ink tank 31 by the tank moving mechanism 41 (ACT S8), if the ink surface
in the lower-stream side ink tank 31 does not rise by a prescribed height
(NO in ACT S7). For example, the control section 43 drives the tank
moving mechanism 41 so that the height difference h2 shown in the FIG. 5
becomes five times the height difference h1.

[0082] When the height difference h2 reaches at five times the height
difference h1, the proper pressure value Pn of the nozzle 85 becomes -5
(kPa). That is, the negative pressure in the nozzle 85 further increases
and thus the ink remaining in the pressure chamber 67 is discharged.

[0083] On the other hand, if the ink surface in the lower-stream side ink
tank 31 rises at a prescribed height (YES in ACT S7) or a given time
elapses after the height difference h2 comes five times the height
difference h1 (YES in ACT S9), the control section 43 returns the
lower-stream side ink tank 31 to the standby position by the tank moving
mechanism 41 (ACT S10). In other words, the tank moving mechanism 41
moves the lower-stream side ink tank 31 so that the height difference h2
comes to be equal to the height difference h1.

[0084] Next, the upper-stream side open/close valve 15 is set at the open
position (ACT S11), and ink is charged to the pressure chamber 67 of the
ink jet head 11. As described above, the ink in the upper-stream side ink
tank 23 is fed to the pressure regulation tank 17 and thus the ink in the
pressure regulation tank 17 is conveyed to the ink jet head 11 by
activating the upper-stream side air pump 25 (ACT S12).

[0085]FIG. 11 is a sectional view illustrating a state that the pressure
chamber 11 and the nozzle 85 of the ink jet head 11 are empty. FIG. 12 is
a sectional view illustrating a state in which ink is supplied to the
pressure chamber 67. FIG. 13 is a sectional view illustrating a state in
which ink is further supplied to the pressure chamber 67. FIG. 14 is a
sectional view illustrating a state that ink is filled in the pressure
chamber 67. FIG. 15 is a sectional view illustrating the ink jet head 11
which performs the purge action.

[0086] When ink is fed to the ink jet head 11, the ink is supplied to the
pressure chamber 67. The ink supplied flows within the pressure chamber
67, as shown in the FIGS. 11 to 15, to be filled in the pressure chamber
67. That is, a flesh ink stored in the upper-stream side ink tank 23 is
charged to the pressure chamber 67 by the upper-stream side air pump 25,
the upper-stream side ink tank 23 and the pressure regulation tank 17.

[0087] As shown in the FIG. 11, there is a possibility that a caked ink SS
smaller in size than the caked ink SL discharged remains in the pressure
chamber 67. As shown in the FIGS. 12 and 13, charging of ink to the
pressure chamber 67 begins when ink is conveyed to the ink jet head 11.
After that, as shown in the FIG. 14, ink is filled in the pressure
chamber 67. While ink is filled in the pressure chamber 67, the caked ink
SS is forcibly moved toward the nozzle 85 with the ink and the meniscus M
of the ink.

[0088] As shown in the FIG. 4, the height difference h1 becomes -1
(kPa)/ρg by filling ink in the pressure chamber 11 (YES in ACT S13 in
the FIG. 4), the control section 43 stops the upper-stream side air pump
(ACT S14). However, it is not limited to that, and the upper-stream side
air pump 25 may operate continuously.

[0089] After ink is filled in the pressure chamber 67, the above-described
purge action is performed (ACT S15). That is, the control section 43
applies voltage to the electrode 71 by the circuit board 54 of the ink
jet head 11. When the voltage is applied to the electrode 71, the pole
portion 68 is deformed in a shear mode, as shown by the two-dot chain
line in the FIG. 15. The ink filled in the pressure chamber 67 is
pressurized by the shear mode deformation of the pole portion 68.

[0090] As shown by the two-dot chain line in the FIG. 15, the meniscus M
of the ink projects from the nozzle 85 of the ink jet head 11 when the
ink is pressurized. Thus, the ink and the meniscus M of the ink projected
to the outside of the nozzle 85 of the ink jet head 11 discharge the
caked ink SS from the nozzle 85 to the outside of the ink jet head 11.

[0091] After the ink and the meniscus M thereof project to the outside of
the nozzle 85 of the ink jet head 11, the shear mode deformation of the
pole portion 68 is released. As shown by the solid line in the FIG. 15,
when the shear mode deformation of the pole portion 68 is released, the
ink and the meniscus M thereof are returned to the inside of the nozzle
85 of the ink jet head 11. In other words, the ink and the meniscus M
thereof temporarily project to the outside of the nozzle 85 in the purge
action. Then, the maintenance of the printing apparatus 10 is completed
and the bubble B and the caked inks SL, SS which are present in the
pressure chamber 67 and the nozzle 85 are finally discharged.

[0092] Instead of the above-described purge action, ink may be ejected
from the nozzle 85, for example. When the pole portion 68 performs the
shear mode deformation, the ink droplet including the caked ink SS is
ejected from the nozzle 85 and thus the caked ink SS is discharged from
the pressure chamber 67 and the nozzle 85.

[0093] The purge action is not limited to the above but other method may
be adopted. For example, the height difference h1 is decreased by moving
the pressure regulation tank 17, and whereby the ink charged in the
pressure chamber 67 is pressurized and then the ink and the meniscus M of
the ink project to the outside of the nozzle 85.

[0094] It should be noted that the maintenance method of the printing
apparatus 10 is not limited to the above-described method. FIG. 16 is a
flow chart showing another example of the maintenance method of the
printing apparatus 10. As shown in the FIG. 16, the ink in the
lower-stream side ink tank 31 is discharged by activating the
lower-stream side suction pump 35 (ACT S23), instead of moving the
lower-stream side ink tank 31 by the tank moving mechanism 41. By
discharging ink, the gas-liquid boundary surface in the lower-stream side
ink tank 31 moves downward.

[0095] By moving the gas-liquid boundary surface downward, the height
difference h2 becomes four times the height difference hl and the proper
pressure Pn in the nozzle 85 increases to -4 (kPa). When the negative
pressure is increased, the ink in the ink jet head 11 flows as shown by
the arrow in the FIG. 5. The meniscus M of the ink in the pressure
chamber 67 is pulled back because of the flow of ink, as shown in the
FIGS. 6 to 10. The lower-stream side suction pump 35 is stopped when the
height difference h2 becomes four times the height difference h1 (ACT
S25). After that, the lower-stream side suction pump 35 is activated to
further move the gas-liquid boundary surface in the lower-stream side ink
tank 31 downward (ACT S28) if the gas-liquid boundary surface (ink
surface) in the lower-stream side ink tank 31 does not rise at a
prescribed height (NO in ACT S7).

[0096] By the above-described another maintenance method also, the ink
filled in the pressure chamber 67 of the ink jet head 11 is discharged to
the lower-stream side ink tank 31. In this another maintenance method,
the lower-stream side ink tank 31 is an example of a discharge unit and a
combination of the lower-stream side suction pump 35 and the lower-stream
side ink tank 31 is an example of an element which functions as a second
unit. However, the unit which conveys the ink in the pressure chamber 67
to the lower-stream side ink tank 31 is not limited to the combination of
the lower-stream side suction pump 35 and the lower-stream side ink tank
31 but several other units may be adopted.

[0097] According to the printing apparatus 10 having the above
construction, the control section 43 discharges the ink in the pressure
chamber 67 to the lower-stream side ink tank 31 and charges the ink in
the pressure regulation tank 17 to the pressure chamber 67. Furthermore
the control section 43 projects the meniscus M of the ink supplied to the
pressure chamber 67 from the nozzle 85 to the outside of the ink jet head
11. Therefore, the babble B and the caked ink SL, SS existing in the
nozzle 85 are able to flow and thus they are removed from the nozzle 85.
As a result, the surface of the nozzle 85 is wetted with a flesh ink when
print is performed and thus, for example, clogging of the nozzle 85 with
ink whose viscosity is increased, failure of the ink-ejection and the
ink-ejection in an undesired direction are restrained. That is, failure
of printing with the caked ink can be restrained.

[0098] The control section 43 charges ink in the pressure regulation tank
17 to the pressure chamber 67 of the ink jet head 11 to perform the purge
action after discharging ink in the pressure chamber 67 to the
lower-stream side ink tank 31. By discharging the ink to the lower-stream
side ink tank 31 beforehand, it is restrained that the nozzle 85 is
clogged with the caked ink SL. Furthermore, it is also restrained that
bubbles are generated in the pressure chamber 67 and the nozzle 85
because the ink-discharging which causes the suction of air from the
nozzle 85 is carried out beforehand.

Second Embodiment

[0099] A second embodiment will be described with reference to the FIG.
17. In the following embodiment, the same reference numerals in the
Figures are applied to the similar component elements in the FIG. 17
having the same functions as the printing apparatus 10 in the first
embodiment, and therefore, the detailed descriptions in whole or in part
thereof are not repeated.

[0100]FIG. 17 is a block diagram roughly illustrating the constructions
of a printing apparatus 10A according to the second embodiment. As shown
in the FIG. 17, the printing apparatus 10A further includes a circulation
path 121, a second filter 122 and a circulation pump 123.

[0101] The circulation path 121 is connected between the pressure
regulation tank 17 and the lower-stream side ink tank 31. One of the ends
of the circulation path 121 is slightly apart from the ink surface in the
pressure regulation tank 17. The other end of the circulation path 121 is
inserted into the ink in the lower-stream side ink tank 31 such that it
is slightly apart from the bottom surface of the lower-stream side ink
tank 31.

[0102] The second filter 122 is arranged at the circulation path 121. The
second filter 122 removes a foreign substance contained in the ink
flowing from the lower-stream side ink tank 31 to the pressure regulation
tank 17. Therefore, ink from which a foreign substance is removed is
supplied to the pressure regulation tank 17.

[0103] The circulation pump 123 is also arranged at the circulation path
121. When the circulation pump 123 is operated, the ink stored in the
lower-stream side ink tank 31 is conveyed to the pressure regulation tank
17 through the circulation path 121.

[0104] The control section 43 judges whether or not an amount of the ink
stored in the lower-stream side ink tank 31 is increased from the
prescribed amount based on the output of the second hydraulic head sensor
119. If the amount of the ink in the lower-stream side ink tank 31 is
increased from the prescribed amount, the control section 43 activates
the circulation pump 123.

[0105] Then, the ink discharged to the lower-stream side ink tank 31 is
returned to the pressure regulation tank 17 by the operation of the
circulation pump 123. In other words, the ink is circulated through the
pressure regulation tank 17, the ink jet head 11 and the lower-stream
side ink tank 31.

[0106] According to the printing apparatus 10A having the above
construction, the ink stored in the lower-stream side ink tank 31 is fed
to the pressure regulation tank 17 by the circulation pump 123.
Therefore, the consumption amount of the ink is decreased.

[0107] According to the printing apparatus of at least one embodiment
described above, the ink in the pressure chamber is discharged to the
second tank by the discharging device, the ink in the first tank is
charged to the pressure chamber by the supplying device, and the liquid
surface of the ink supplied to the pressure chamber is located at the
outside of the inkjet head from the nozzle, whereby the printing failure
with the caked ink can be restrained.

[0108] The present invention has been described with respect to specific
embodiments. However, these embodiments have been presented by way of
example only. Other embodiments based on the principles of the present
invention should be obvious to those of ordinary skill in the art. Such
embodiments are intended to be covered by the claims.